Electromagnetic telephone receiver



April29, 1947. J. WOLFF 2,419,697

ELECTROMAGNETIC TELEPHONE RECEIVER Filed Nov. 10, 1944 lA/VFNTOR Patented Apr. 29, 1947 ELECTROMAGNETIC TELEPHONE RECEIVER Joachim Wolff, London, England, assignor of one-half to Hettie Dent, London N. 6, England Application November 10, 1944, Serial No. 562,799 In Great Britain November'19, 1943 2 Claims. (Cl. 179114) This invention relates to telephone receivers and whilst being more particularly applicable to small telephone receivers such as those used in deaf aid appliances is applicable to telephone receivers of sizes to which the invention can be applied.

The object of the present invention is to provide a telephone receiver having a single air gap and wherein the case itself forms a part of the magnetic circuit.

A further object of the invention is to provide a telephone receiver of which a single pole is adjustable from the outside so as to enable the air gap and thus the sensitivity of the receiver to be'ad'justed.

Another object of the invention is to provide a telephone in which the total reluctance of the magnetic circuit is considerably reduced, whilst the available energy is increased in corresponding proportion.

A still further object of the invention is to effect a considerable economy in metal, space and overall dimensions of a telephone receiver,

According to the present invention a telephone receiver is provided with a casing of magnetic material and forms a part of the magnetic circuit so as to provide a permanent magnetic flux.

On the base of the casing of the receiver is provided a central pole which is preferably adjustable.

A diaphragm preferably bears at its periphery on the annular wall of the casing of the receiver.

The diaphragm is preferably of thin sheet steel and is preferably thickened at the central portion.

For the purpose of adjusting the pole, this is preferably adjustably mounted in a split sleeve of soft iron, mounted in the base of the casing.

The casing is preferably of polarised hardened steel.

In cases when superimposed D. C. flows through the receiver the casing is preferably of soft iron.

The invention will now be described by way of example with reference to the accompanying drawing, wherein- Fig. l is a vertical section of a telephone receiver.

Fig. 2 is a plan of Fig. 1.

Fig. 3 is a section on the line IIIIII of Fig. 1.

As shown in the drawing a telephone receiver is provided with a circular casing 2 which when A. C, only is passed through the receiver is of polarised hardened steel or steel alloy, and may be of soft iron when D. C. also flows through the receiver, such as is the case for example when the receiver forms part of a deaf aid appliance. In the centre of the base 3 of the casing 2 is secured a sleeve 3 of soft iron which is slit preferably on diametrically opposite portions of its wall I0, as indicated at II, as to provide oppositely located portions which normally tend to approach one another under their natural resiliency.

The sleeve 3 is provided with an internally screw threaded portion which is engaged by a screw threaded portion I2 on a central pole 4 of soft iron which is fitted into the sleeve 3.

One end ofthe screw threaded portion I2 is suitably shaped or isprovided with an opening or slot I3 for engagement by'a suitable tool for adjusting the pole 4 in the sleeve 3.

In the construction shown the sleeve 3 has a bore of two different diameters, the portion of the bore of smaller diameter being screwthreaded internally and the portion of the sleeve 3 containing this portion passes through the base 9 of the casing 2 in which it is secured in any suitable manner, such as by expanding as shown at I4.

The portion of sleeve 3 with the bore portion of larger diameter is slit as shown at I I on opposite sides for substantially the whole of its length.

The pole 4 is provided with a reduced portion which is screw threaded as indicated at l2 for engagement with the screw threaded portion of the bore'in the sleeve 3.

After the pole 4 has been adjusted the opening I 4' in the sleeve 3 through which the adjustment is effected may be sealed.

Around the sleeve 3, I0 is placed a speech coil 6 wound on a bobbin 5.

On the casing 2 is placed a steel diaphragm I, this diaphragm I bearing at its periphery on the top of the annular wall of the casing 2 on which it is held by a cover I screwed on the casing.

The cover I is provided with a central opening I5 and bears against the periphery of the diaphragm I through a packing ring 8.

The diaphragm I is of steel and on its face adjacent the central pole 4 is thickened at its central area, the thickening bleing preferably formed by soldering or welding a thin steel disc I6 thereto. In this manner the reluctance of the diaphragm I is reduced, whilst the natural frequency of the diaphragm I is displaced to a desirable position in the frequency band.

By means of the construction above described it will be appreciated that a considerable economy in metal, space and overall dimensions is ob- 3 tained as a separate outer casing for accommodating the magnet system is not required.

As the central pole 4 is adjustable from the outside after all the parts of the receiver have been assembled, the sensitivity of the receiver can be readily adjusted after which it can be sealed.

There is only one airgap between the diaphragm I and the magnet system, as the diaphragm I rests permanently on the annular wall of the casing 2, which forms a component of the closed magnetic circuit. The reluctance of the magnetic circuit is thus considerably reduced, Whilst the available energy is increased in corresponding proportion.

I claim:

1. In a telephone receiver the combination with a circular casing having a centrally apertured bottom and an open top, and a diaphragm located over said open top, of a resiliently split sleeve of soft iron secured centrally in said centrally apertured bottom, and a pole adjustably mounted in said split sleeve, a bobbin surrounding said split sleeve, two flanges of different diameter on said bobbin, the smaller flange bearing against the bottom of said casing, said larger flange being spaced at a short distance from the wall of said casing, and a coil mounted on said bobbin.

2. A telephone receiver comprising a casing of magnetic material having a centrally apertured bottom and an open top, a circular diaphragm bearing at its periphery on the open end of said casing, a cover screwing over the open top of said casing and securing said diaphragm to said casing, a packing ring between said cover and said 15 inner wall of said casing, and a coil around said diaphragm, said diaphragm having its central portion thickened, a sleeve secured centrally in said centrally apertured bottom, said sleeve having a bore of different diameters, the bore of smaller diameter being screwthreaded, the portion of the sleeve having the larger diameter bore being split at diametrically opposite points so as to render it resilient, a pole mounted in said larger diameter bore, a screwthreaded portion on said pole engaging said screw-threaded bore, a bobbin surrounding said sleeve, two flanges of difierent diameter at opposite ends of said bobbin, the flange of smaller diameter bearing against the centrally apertured bottom, the flange of larger diameter being slightly spaced from the bobbin between said flanges.

JOACHIM WOLFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,026,196 Beck May 14, 1912 1,096,127 Rosenberg May 12, 1914 1,542,746 Timmons June 16, 1926 1,639,546 Wieland Aug. 16, 1927 2,064,426 Greibach Dec. 15, 1936 1,283,304 Rhodus Oct. 29, 1918 1,403,592 Coy Jan. 17, 1922 FOREIGN PATENTS Number Country Date 214,787 British May 1, 1924 

